The NFLPA has already said Miller's suspension is not because of a violation of the league's policy on performance-enhancing drugs.

Because of the league's confidentiality clause, Miller was quiet about what the suspension was in regards too when the ban came down last month. The same went for Broncos' coach John Fox.

Denver opens preseason play Thursday night against the San Francisco 49ers. Miller is eligible to play in all four of the Broncos preseason games. If Miller's appeal is not successful, the suspension begins August 30—the day after the Broncos' last preseason game.